net: mqtt: Maintain count of PINGREQ awaiting response

Maintain a simple count of how many PINGREQ have been sent for the
current connection that have not had a corresponding PINGRESP.  Nothing
is done with this information internal to the MQTT driver, but it is
exposed to the application layer to monitor as desired.

Signed-off-by: Justin Brzozoski <justin.brzozoski@signal-fire.com>
3 files changed